The effect of postural drainage (PD) on the acute and chronic course of cystic fibrosis (CF) is unclear. To date, no studies have been reported on the adaptation of the CF patient to submaximal exercise, and there is only one report on the adaptation to maximal exercise. Although exercise is thought to increase sputum expectoration and improve pulmonary functions in CF patients, this has not been well documented. The purpose of this project is to: (1) Describe in detail the physiological adaptation of CF patients to incremental exercise; (2) Compare the effectiveness of PD and exercise in the treatment of the CF patient on lung function; and (3) Observe the effects of a regular, prescribed, home-exercise program on pulmonary functions and work capacity. In the first study, patients with different severities of CF will have their adaptations to incremental exercise assessed. Severity of CF will be determined by measuring clinical symptoms and signs, and pulmonary functions. Adaptations to exercise will be evaluated by measuring oxygen uptake, CO2 production, minute ventilation, endtidal gases, arterial-oxygen saturation, heart rate, and ECG at progressively increasing work rates. CF patients' response will be compared with that of age-matched normals. In the second study, the effects of either three-times-daily PD or two-times-daily exercise over two weeks repeatedly performed (every 1-2 hrs.) daily pulmonary functions and sputum production will be studied in the hospital. Work capacity will be measured in both groups at the beginning and at the end of the two-week period. Finally, on the basis of the above studis, a group of patients will be selected for a home-exercise program, to be done daily for two months. Pulmonary functions and work capacity will be assessed before, during, and after each of the test periods.